1. Field of the Invention
The invention relates to a process for utilizing a feedstock comprising nitrogen-organic compounds to a useful end purpose. The feedstock is subjected to gasification at pressure and a temperature of at least about 900xc2x0 C., using a gasifying medium containing free oxygen, the gasification being as a flame reaction in an entrainedxe2x80x94bed gasifier. Apparatus for carrying out the process is provided as well. The invention can be used for the harmless utilization of nitrogen-organic compounds by gasification, generating a gas containing carbon monoxide and hydrogen.
2. Description of the Related Art
Nitrogen-organic compounds, and in particular residual and waste substances of the chemical industry, are to be understood as meaning mixtures of amines, nitrites or other nitrogen-containing hydrocarbons which could occur as waste substances or residues of the intermediate products of chemical syntheses but, for a wide variety of reasons, cannot be further processed directly, for example as mixed products.
It is known to incinerate carbon-containing residual and waste substances, utilizing the heat produced. If, however, such materials consist completely or partly of nitrogen-organic compounds, nitrogen oxides are formed to a great extent during the incinerating operation, pass into the atmosphere with the exhaust gases and contribute significantly to the acidification of rainwater. In recent years, a large number of catalytic and non-catalytic processes have been developed and leading in the case of high NOx concentrations, to considerable costs for the removal of the nitrogen oxides from the flue gas. The hot and voluminous amounts of flue gas require large dimensioning of the apparatus and equipment provided for the removal of the nitrogen oxides. An extensive summary of the prior art is provided by W. Fritz et al, xe2x80x9cReinigung von Abgasenxe2x80x9d [cleaning of exhaust gases], Vogel Buchverlag, Wxc3xcrzburg 1992.
In the technique of gas generation, the gasification of fuels and of residual and waste substances which are in a free-flowing state, or can be transformed into this state, by partial oxidation in an entrained bed is known. In this case, the material being gasified and the gasifying medium, such as air, oxygen-enriched air or industrial oxygen, and optionally mixed with water vapor, and often also under increased pressure, are transformed in the form of a flame reaction into a gas rich in carbon monoxide and hydrogen. The raw gas produced under these conditions is used after appropriate cooling and cleaning as a synthesis gas or for energy-related purposes.
It is therefore the object of the invention to provide a way of harmlessly utilizing nitrogen-organic compounds which does not have the disadvantages of the prior art.
It has been found unexpectedly that, in spite of the highly reducing atmosphere present in the entrained-bed reactor, even under relatively high pressures, the nitrogen-organic compounds are oxidized to neutral nitrogen N2. Further oxidation stages are not reached; therefore there are no detectable amounts of nitrogen oxides in the gasifying gas. The expected formation of ammonia NH3 due to the already described high reduction potential of the gasifying gas also surprisingly does not occur. The concentration of the ammonia in the gasifying gas is around the same level as that known from coal and oil pressure gasification.
The solution according to the invention provides a process for the utilization of a feedstock essentially comprising nitrogen-organic compounds in such a way that the utilization takes place by gasifying under normal pressure or increased pressure, it being advantageous to use a pressure of up to 40 bar. The temperatures during the gasifying process should be at least about 900xc2x0 C. and preferably in the range of about 1100 to about 1600xc2x0 C. as a suitable range for the partial oxidation using a gasifying medium containing free oxygen.
It is advantageous to perform the gasification by partial oxidation as a flame reaction in an entrained-bed gasifier.
It is also advantageous for the utilization of nitrogen-organic compounds to take place in the following technological stages: Feeding into an entrained-bed gasification. In this case it is advantageous to use an entrained-bed gasifier with a refractory-lined reactor chamber.
Taking place as the next stage is the partial cooling of the hot raw gas by spraying in water in the quenching process.
Provided as a further stage is a high-pressure steam generation further cooling the gas, then effecting, a gas COS hydrolysis, and a HCN hydrolysis, a desulfurization and a waste water treatment all being done in a succession downstream of the high-pressure stream generation.
It also is advantageous for ammonia separated in the waste water treatment to be returned to the gasifying reactor for disposal. In the process, different nitrogen-organic compounds are fed to the gasifying reactor together or separately and are gasified simultaneously. It is also possible with the process for organic and inorganic nitrogen compounds to be gasified together.
The apparatus for carrying out the process includes an entrained-bed gasifier into which a feedstock of nitrogen-organic compounds are fed, gasification of nitrogen compounds occurring in the entrained-bed gasifier. A quencher which cools and quenches the hot raw gas outletting the entrained-bed gasifier is located immediately downstream of the bed gasifier. A waste water treatment unit is connected by piping to the quencher so that spent or waste water used in the cooling and quenching of the hot raw gas can be delivered to the treatment unit. Next downstream of the quencher is a high-pressure steam generator through which the still heated raw gas passes for further cooling thereof and incident said cooling, steam being generated in the generator. The raw gas passes from the high pressure generator to a downstream hot-gas filter stage wherein certain fractions are filtered out of the gas before it passes next downstream to a COS/HCN hydrolysis unit. The raw gas then passes through a low-pressure steam generator for further cooling thereof following which there is still another cooling stage wherein the gas is cooled. The gas then is passed to a desulphurization stage for producing clean gas and sulphur draw off. A pipe connects the waste water treatment with the bed gasifier so that ammonia generated in waste water treatment can be returned to the gasifier for disposal.
The apparatus also includes piping providing that water outletting the low pressure stream generator and the low-pressure stream generator post cooling of the raw gas, be supplied upstream to the quenchers for use therein.